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arXiv · 2507.00450

Shell effects in quasi-fission for calcium induced reactions forming thorium isotopes

C. Simenel·A. S. Umar·K. Godbey·P. McGlynn
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Abstract

Quantum shell effects induce an asymmetric fission mode in actinides, which disappears in neutron deficient isotopes. Quasi-fission, characterized by a significant mass transfer in heavy ion collisions at low-energies, is expected to be affected by similar shell effects. This is studied in 40-56Ca+176Yb reactions with the time-dependent Hartree-Fock approach. All reactions exhibit a mass equilibration process that stops when a heavy fragment with Z~54 protons is formed. Unlike the fission of thorium compound nuclei, quasi-fission does not exhibit a transition to symmetric modes in neutron deficient systems. This observation is interpreted in terms of potential energy surfaces that show a persistence of an asymmetric valley with an increasing barrier preventing its population in fission of the most neutron deficient thorium isotopes.

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C. Simenel, A. S. Umar, K. Godbey, P. McGlynn. 2025-07-01. Shell effects in quasi-fission for calcium induced reactions forming thorium isotopes. https://doi.org/10.1016/j.physletb.2025.139955

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